ASSAYING. 



127 



that it makes no perceptible difference whether 100 or 1,000 grains of lead 

 are used with .1 grain of silver. It has been pointed out that the loss of 

 silver is compensated for in small buttons by the lead retained and it would 

 seem that this ought to be equally true of large ones, but as a matter of 

 fact it is not, probably because large buttons remain for a longer time 

 melted, thereby being more completely cupelled. As the silver contained 

 in any of the country rocks of Eureka District scarcely ever reached 50 

 cents to the ton (0.001325 per cent.) the assays can be regarded as unaffected 

 by any loss in cupellation An experiment was made to test this inference, 

 and it was found that there was no perceptible loss in cupelling 50 cents 

 (.005 grain) of silver with 400 grains of lead at a temperature considerably 

 above that required for proper cupellation. 



Experiments. — In regard to the loss by cupellation in general the following 

 experiments may be of interest as showing the differences in loss at various 

 points in the muffle. 



Nine assays, each containing 5 grains silver and 30 grains lead, were 

 cupelled and the losses expressed in thousandths of the unit of 5 grains 

 attending each, with the number of the assay, are shown in the diagram of 

 the muffle in the position occupied by the corresponding cupel: 



Back of muffle. 



FlG. 3. — Position of cupels iu muffle. 



The order 9, 6, 3, 2, 8, 5, 7, 4, 1 represents the order in which the 

 cupels were withdrawn from the muffle, and therefore the speed at which 

 the cupellation took place. Nos. 7, 8, and 9 were cupelled at the proper 

 temperature, but those in the back part of the muffle were too hot. It will 



